1. Field of the Invention
The present invention relates to an apparatus and a method for depositing encryption keys such as private keys of a public key cryptosystem with depositaries.
2. Description of the Related Art
Confidentiality of information is ensured illustratively by encrypting it with a public key cryptosystem. Such encrypted information cannot be decrypted without recourse to suitable private keys. Where general security of an individual is concerned, no encrypted information belonging to that individual can be decrypted by use of a private key if the individual is for some reason unable to access the system (due to absence, illness, death, etc.). Since the inability to access the system obviously means that any access to the information therein is denied, it no longer matters whether the individual can use his or her private key. Because the information belongs to the individual who owns the private key, there is no need in such a case to make arrangements for any other individual to gain access to the information.
Things are different where corporate security is involved. The unavailability of a private key to any party other than the individual who owns it can be a problem. Individuals working for a company play their respective roles in the organization's activities. Information about corporate activities is necessary for the firm whether or not any such information is encrypted by private keys belonging to specific workers. If encrypted corporate information cannot be decrypted when needed because an individual worker with a private key to the information is out of office, on sick leave or has deceased, an appropriate in-house proxy must be allowed to access the information so that business will proceed unimpaired.
Mechanisms for depositing private keys with depositaries have existed but they have posed the following problems:
1) Whether or not to deposit private keys with depositaries is left to the discretion of the owners of the keys. Of course, rules could be established to stipulate the deposition of private keys, but there is no guarantee that such rules are strictly observed throughout a system. Nor is there any way of verifying whether deposited private keys are legitimate keys.
2) Selection of depositaries is at the discretion of private key owners. Unless a private key is deposited with a competent depositary, the deposited key is unavailable in case of an emergency. A malicious depositary can abuse the entrusted private key.
3) Procedures of deposition are complicated. Generally, an original private key is divided into a plurality of parts that are stored on a plurality of portable storage media such as floppy disks. The storage media are then deposited with a plurality of depositaries. The procedures are troublesome to both the key owner and the depositaries.
4) Management of entrusted private key parts is left to the discretion of depositaries. Inadequate management by the depositaries can lead to the abuse of a key by an unscrupulous third party.
5) The depositaries designated by a private key owner can conspire to restore and use or abuse the private key without knowledge of the owner. The right of the legitimate key owner can thus be infringed on, and the security of electronic signatures can be compromised.
6) Once a private key is reconstituted, the party or parties that restored the key will permanently possess the same right of access as the original private key owner. This will result in an infringement of the right of the legitimate key owner and compromise the security of electronic signatures.
It is therefore an object of the present invention to overcome the above and other deficiencies of the prior art and to provide an apparatus and a method for implementing a systematically controlled scheme of depositing private keys with depositaries and of sufficiently guaranteeing the security of entrusted private keys.